Controlling the size of your image elements is a useful skill no matter what you’re making in GIMP, and it’s really easy to do. If you’re used to working in Photoshop, you might have had a hard time finding the equivalent of the Free Transform tool in GIMP, but it just has a different name!
The Unified Transform tool will let you do free transforms in GIMP almost exactly the same way as you’re used to in Photoshop. You can find it easily in the toolbox panel or switch to it instantly with the keyboard shortcut Shift + T (Command + T if you’re using GIMP on a Mac).
Once you select the Unified Transform tool, click anywhere on your image and GIMP will overlay a series of handles along the edges of your image, as you can see in the screenshot above.
These handles each have their own effect. Square handles apply scale transforms, large solid white diamonds for shearing adjustments, and small outlined diamonds for perspective transform. Clicking anywhere outside the image on a section of blank workspace allows rotation around the designated pivot point (more on that later).
If it feels like a lot to remember at first, don’t worry!
The trick to using the Unified Transform tool is paying close attention to what happens to your mouse cursor as you move it over the different handles around the edges of your image. The cursor switches to indicate which action will be performed when you click, so it’s a good idea to get familiar with the toolbox options stacked with Unified Transform.
The other essential feature of the Unified Transform tool is the popup overlay window. It features the Transform Matrix, which showcases the exact transform that has been applied to the image so you can recreate it later.
Below are the key buttons of the Transform Matrix:
- Reset – unsurprisingly, this button simply resets any changes you’ve made.
- Readjust – maintains your transformation changes but resets the transform matrix, essentially applying your transform and then starting a new transform immediately afterward.
- Transform – this applies the current transform settings to your current image layer (or linked layers)
Setting the Pivot Point
The other specialized handle that you’ll see while using the Unified Transform tool is the central pivot point, represented by a quartered circle in the very center of your image:
This pivot point is more or less exactly what you’d expect: it acts as the central point for any rotational transformations. The cool part is that you can click and drag to place it anywhere you want, including snapping it to the edges or corners as needed.
As with many tools in GIMP, you can modify the effects of the Unified Transform tool by combining clicks with the Ctrl, Alt, and Shift keys (Command, Option, and Control if you’re using a Mac). If you take a close look at the Tool Options panel below, you’ll see the various effects:
There are also a couple of options that are generally applied to all of GIMP’s transform tools, but they’re simple enough to understand, and probably won’t be necessary for most of your transform usage unless you have very specific requirements.
Direction is useful for certain corrective adjustments, but leaving it at the Normal (Forward) setting is correct for 99% of use cases. Corrective (Backward) is intended to allow you to perform geometric corrections such as in an improperly positioned scanned image.
I did find that switching between the two has produced some very undesirable and confusing results in my testing, so I’d recommend just leaving this setting alone unless you’re certain it’s what you need to use.
It actually might take an entire article in itself to discuss all the various corrective applications, but it’s a very cool tool if you take the time to explore it.
The Interpolation setting controls how pixel data is created or compressed when changing size. Generally, the default Cubic setting is best, but None and Linear are very fast and low quality while LoHalo and NoHalo are much more CPU-intensive due to their halo reduction algorithms, but they can produce better results than Cubic in certain situations.
Clipping allows you to determine what happens to your image after you’re finished with your free transform and you’ve applied it. Depending on exactly what your transformation did, your image content may extend beyond the original borders of the layer and/or image.
Adjust expands your layer to match the newly adjusted size, Clip discards image data outside the layer/image boundaries, and Crop to result reduces the image size to discard all transparent pixels created by the transform. Crop to aspect does the same but locked to the original aspect ratio.
Last but not least, there are the Guides. These provide a wide range of guide overlays that are superimposed over your image to help you guide your composition, covering everything from the standard Rule of Thirds used in photography to the diagonal lines shown above or a totally customizable grid.
That’s about all there is to know about how to free transform in GIMP! Once you know to look for the Unified Transform tool instead of Free Transform, it’s fairly easy to use, but a bit of practice – and a helpful guide – can make all the difference in your workflow.
Happy editing!About Thomas Boldt